Rocket engine nozzles are currently configured in two general shapes, conical and ramp configuration, both in various sizes and materials to suit the high temperature and pressure environment for which they are designed. A common design for conical shaped rocket nozzles provides a single pass, multiple brazed-tube nozzle wall. A plurality of tubes are joined side-to-side to form an outer wall of a nozzle wherein the tubes also act as flow channels for the combustion fuel. Combustion fuel enters each of the tubes from a manifold, is preheated as it traverses the tubes, and simultaneously acts to cool the nozzle. This conventional design includes a plurality of circular tubes numbering approximately 1,000 to approximately 1,100 tubes. The individual tubes are drawn and swaged such that a diameter of each tube decreases and its wall thickness increases from a nozzle discharge end to a nozzle inlet end. This conventional tube design includes materials that are difficult to weld, particularly in a tube-wall to tube-wall configuration. A brazing process is therefore used to join the tubes. Each of the drawn and swaged tubes is first coated with a nickel material which is suitable to braze the plurality of tubes in a side-to-side configuration. The swaged and coated tubes are arranged having the larger diameter ends adjacent to one another to form the nozzle conical shape and the arrangement is collectively furnace brazed.
One drawback of brazed rocket nozzles is that repair of reusable nozzles is difficult and expensive. The heat of combustion as well as the number of cycles of heating and cooling that a reusable nozzle is subjected to cause the materials to fatigue and crack. Because the tube materials are difficult to weld, nozzle repair is generally limited to brazing techniques on each tube. Brazing of individual tubes is time consuming and often incapable of repairing large cracks. If a tube cannot be braze-repaired, the tube is sealed. When a specified percentage of tubes are sealed, the nozzle can no longer be used.
A common rocket nozzle has a diameter of approximately 76.2 cm (30 in) adjacent to the main combustion chamber of the rocket engine. The large diameter or distal end of the nozzle has approximately a 183 cm (6 ft) diameter. A further drawback of the brazed nozzle design is that attempts to repair a nozzle of this size itself creates problems in that heat input during the repair process can create sequential problems with the brazed material in adjacent or local tubes.
A further drawback of the common brazed nozzle design is that the brazed joint is the weakest link. Even a small rupture in a brazed tube-to-tube joint can result in either reduced cooling at the upper nozzle (i.e., adjacent to the combustion chamber) or a leak of preheated fuel into the nozzle flame, either of which can result in catastrophic nozzle failure.
A need therefore exists for a nozzle design providing a repairable configuration which does not rely on the brazing process. A need also exists to replace the tube-to-tube design commonly used with a configuration which is easier to form and which permits either repair of individual flow channels or replacement of segments of flow channels.